Module bypass switch for balancing battery pack system modules with bypass current monitoring

ABSTRACT

A battery pack system module may include a module bypass switch for allowing charge current to bypass the battery pack system module. The module bypass switch may be activated to divert charging current from the battery pack system module to other battery pack system modules. The charging current may be diverted to bring other battery pack system modules into balance with the battery pack system module. That is, to bring the state of charge of all battery pack system modules into coarse balance. When the module bypass switch is activated, charging current through the module bypass switch may be monitored by a current sensing device such as a current sensing resistor. A microprocessor may receive information about the bypass current level and use the information to determine when to de-activate the module bypass switch. Sensing current through a module bypass switch allows more accurate and quicker inter-module balancing.

PRIORITY CLAIM

This application is a divisional of U.S. patent application Ser. No.13/494,502 to David A. White et al. entitled “Module Bypass Switch withBypass Current Monitoring” filed on Jun. 12, 2012, which claims priorityto U.S. Provisional Patent Application No. 61/498,358 to David A. Whiteet al. entitled “Module Bypass Switch for Balancing Battery Pack SystemModules with Bypass Current Monitoring” and filed on Jun. 17, 2011, allof which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure generally relates to a system for balancing aplurality of battery pack system modules.

BACKGROUND

A device powered by rechargeable batteries may include several batterycells to achieve the voltage and/or current levels used by the device.For example, if a rechargeable battery cell has a nominal output voltageof 1 Volt, the a device having a 2 Volt operational level may includetwo battery cells placed in series. In another example, if arechargeable battery cell has a nominal output current of 100 milliamps,then a device having a 400 milliamp operational level may include fourbattery cells in parallel. Battery cells in parallel and series may becombined to reach the operational levels of the device.

The battery cells may be grouped with circuitry for balancing the chargelevels in the battery cells to form a battery pack system module.Multiple battery pack system modules may be combined in series orparallel to further increase the output voltage and output currentavailable to a device coupled to the battery pack system modules.Although battery cells within a battery pack system module may bebalanced by using balancing circuitry within the battery pack systemmodule (referred to as intra-module balancing), there is a need forbalancing battery pack system modules to other battery pack systemmodules (referred to as inter-module balancing).

One conventional solution for providing inter-module balancing includesshorting out a battery pack system module within a battery pack systemwith a bypass switch. FIG. 1 is a block diagram illustrating aconventional battery pack system module with a bypass switch. A batterypack system 100 includes battery pack system modules 110, 130. Themodule 110 includes a first group of battery cells 114 having a batterycell 116 coupled in parallel with a battery cell 118. The module 110also includes a second group of battery cells 124 having a battery cell126 coupled in parallel with a battery cell 128. The first group 114 iscoupled in series with the second group 124.

When a bypass switch 112 activates, current through the module 110 isdiverted away from the battery cells 116, 118, 126, and 128. To preventshort circuiting of the battery cells 116, 118, 126, and 128, a resistor120 is coupled in series with the switch 112. However, the resistor 120consumes power and generates heat in the system 100 through Jouleheating. The heat generated by the resistor 120 may result in dangerousconditions within the system 100. For example, the heat may lead to afire involving the battery cells 116, 118, 126, and 128.

Heat generated by the resistor 120 may be problematic where the system100 is operating in an isolated environment. For example, on an underseavehicle such as a submarine, battery pack systems may be isolated in apressurized compartment. Thus, heat dissipated by the resistor 120 maynot be carried away and result in dangerous conditions for the vehicleand operator of the vehicle.

Additionally, when one of the modules 110 or 130 of the system 100becomes defective, the defective module may be replaced with a newmodule. The new module may be at a significantly different charge thanexisting modules of the system 100. In a conventional system, balancingof the replacement module with the existing modules may occur over along period taking days or weeks to reach balance. During this time thesystem 100 may be unavailable for use. In the above example if onemodule in the vehicle is replaced, the vehicle may not be ready foroperation until the modules are fully-charged and balanced. If thebalancing operation consumes days or weeks, the vehicle may be out ofservice for this entire time period.

Conventionally, current through a bypass switch of a battery pack systemmodule is not monitored. However, monitoring the current may allowcapture of information regarding other battery pack system moduleswithout establishing a separate communications bus. The informationobtained from other battery pack system modules may allow faster andmore accurate charging of the battery pack system modules.

SUMMARY

According to one embodiment, an apparatus includes a first battery packsystem module. The apparatus also includes a battery cell coupledbetween a first terminal and a second terminal. The apparatus furtherincludes a charge switch coupled in series with the battery cell and thefirst terminal for interrupting charging of the battery cell. Theapparatus also includes a discharge switch coupled in series with thecharge switch and the first terminal for interrupting discharging of thebattery cell. The apparatus further includes a module bypass switch forshorting the first terminal and the second terminal. The apparatus alsoincludes a current measurement device coupled between the module bypassswitch and at least one of the first terminal and the second terminal.

According to another embodiment, a method includes bypassing a chargingcurrent through a module bypass switch of a first battery pack systemmodule without charging battery cells of the first battery pack systemmodule. The method also includes monitoring the charging current throughthe module bypass switch of the first battery pack system module. Themethod further includes detecting, during the bypassing, that thecharging current has fallen below a threshold value. The method alsoincludes stopping the bypassing of the charging current through themodule bypass switch of the first battery pack system module when thecharging current has fallen below the threshold value.

According to yet another embodiment, a computer program product includesa non-transitory computer-readable medium having code to bypass acharging current through a module bypass switch of a first battery packsystem module without charging battery cells of the first battery packsystem module. The medium also includes code to monitor the chargingcurrent through the module bypass switch of the first battery packsystem module. The medium further includes code to detect, during thebypassing, that the charging current has fallen below a threshold value.The medium also includes code to stop the bypassing of the chargingcurrent through the module bypass switch of the first battery packsystem module when the charging current has fallen below the thresholdvalue.

According to one embodiment, an apparatus includes a first battery packsystem module. The module includes a battery cell coupled between afirst terminal and a second terminal. The module also includes a chargeswitch coupled in series with the battery cell and the first terminalfor interrupting charging of the battery cell. The module furtherincludes a discharge switch coupled in series with the charge switch andthe first terminal for interrupting discharging of the battery cell. Themodule also includes a module bypass switch for shorting the firstterminal and the second terminal.

According to another embodiment, a method includes charging a firstbattery pack system module with a charging current. The method alsoincludes detecting, during the charging, that the first battery packsystem module has reached a first criteria. The method further includesstopping charging of the first battery pack system module afterdetecting the first battery pack system module has reached the firstcriteria. The method also includes stopping discharging of the firstbattery pack system module after detecting the first battery pack systemmodule has reached the first criteria. The method further includesactivating a module bypass switch to pass the charging current throughthe first battery pack system module without charging the first batterypack system module after stopping discharging of the first battery packsystem module.

According to yet another embodiment, a computer program product includesa computer-readable medium having code to monitor a first battery packsystem module. The medium also includes code to disable charging of thefirst battery pack system module when a first criteria is met. Themedium further includes code to disable discharging of the first batterypack system module when a first criteria is met. The medium alsoincludes code to enable passing charge current through the first batterypack system module when the first criteria is met. The medium furtherincludes code to re-enable charging of the first battery pack systemmodule when a second criteria is met.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter that form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiments disclosed may be readily used as a basis formodifying or designing other structures for carrying out the samepurposes of the present invention. It should also be realized by thoseskilled in the art that such equivalent constructions do not depart fromthe spirit and scope of the invention as set forth in the appendedclaims. The novel features that are believed to be characteristic of theinvention, both as to its organization and method of operation, togetherwith further objects and advantages will be better understood from thefollowing description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, referenceis now made to the following descriptions taken in conjunction with theaccompanying drawings.

FIG. 1 is a block diagram illustrating a conventional battery packsystem module with a bypass switch.

FIG. 2 is a circuit schematic illustrating an exemplary battery packsystem module having charge, discharge, and bypass module switchesaccording to one embodiment.

FIG. 3 is a block diagram illustrating an exemplary battery pack systemhaving series and parallel coupled battery pack system modules accordingto one embodiment.

FIG. 4 is a flow chart illustrating an exemplary method of charging abattery pack system module according to one embodiment.

FIG. 5 is a block diagram illustrating an exemplary battery pack systemhaving inter-module communication according to one embodiment.

FIG. 6 is a block diagram illustrating an initializer for an exemplarybattery pack system according to one embodiment.

FIG. 7 is a flow chart illustrating an exemplary method of charging abattery pack system according to one embodiment.

FIG. 8 is a block diagram illustrating a software application formonitoring a battery pack system according to one embodiment.

FIG. 9 is a circuit schematic illustrating an exemplary battery packsystem module having charge, discharge, and module bypass switch andbypass switch current monitoring according to one embodiment.

FIGS. 10A and 10B are a flow chart illustrating an exemplary method ofcharging a battery pack system module with bypass switch currentmonitoring according to one embodiment.

DETAILED DESCRIPTION

A battery pack system having a plurality of battery pack system modulesmay be inter-module balanced by including a module bypass switch, acharge switch, and a discharge switch in the battery pack systemmodules. A charge switch within the battery pack system module may beused to prevent charge current from passing through the battery cells ofthe battery pack system module. When one battery pack system module of abattery pack system is unbalanced with other battery pack system modulesof the battery pack system, the module bypass switch may be activated toallow charge current to bypass the unbalanced battery pack system moduleor modules. A discharge switch within the battery pack system module maybe used to prevent discharge current from passing through the batterycells of the battery pack system module when the bypass module switch isactivated.

De-activation of the discharge switch in the battery pack system moduleprevents shorting of the battery cells in the battery pack systemmodule, which would otherwise occur when the bypass module switch isactivated. Because the discharge switch physically disconnects thebattery cells from terminals of the battery pack system module andbecause there is no resistor in series with the bypass switch as inconventional battery balancing techniques, little to no power isdissipated during inter-module balancing when the bypass module switchis activated. The reduction in the dissipated power reduces heatgenerated in the battery pack system module, and reduces safety hazardsexperienced by the battery pack system and the operator of a deviceincluding the battery pack system.

The module bypass switch enables rapid balancing of battery pack systemmodules within a battery pack system without time-consuming and costlymaintenance operations. Because the battery pack system modules arebalanced during each charging of the battery pack system, the operationof the battery pack system presents reduced safety hazards to operatorsof equipment including the battery pack system. That is, over-chargingof battery pack system modules within the battery pack system is reducedor eliminated, which reduces fire hazards in the battery pack system.Additionally, the balancing of the battery pack system modules throughinter-module balancing during charging operations extends the life ofthe battery pack system modules and reduces replacements costs foroperating equipment including the battery pack system module.

Balancing battery pack system modules through the module bypass switchallows balancing to occur faster than in conventional battery balancingtechniques. Conventional battery balancing devices may re-directcharging currents on the order of hundreds of milliAmps. By providing alow resistance path through the module bypass switch, the magnitude ofre-directed current may be many times higher, such as 10 to 100 Amps.Thus, when a battery pack system module is out of balance from otherbattery pack system modules in a battery system, the balancing operationis completed faster. For example, a balancing operation that may takeseveral hundred hours under a conventional balancing system may becompleted in several hours or less.

FIG. 2 is a circuit schematic illustrating an exemplary battery systemmodule having charge, discharge, and bypass module switches according toone embodiment. Battery cells 212, 214, 216, and 218 are coupled inseries with each other. Although not shown, additional battery cells maybe coupled in series or in parallel with the battery cells 212, 214,216, and 218. A positive battery terminal 202 and a negative batteryterminal 204 are coupled with the battery cells 212, 214, 216, and 218.According to one embodiment, a load (not shown) may be coupled betweenthe terminals 202 and 204 to receive an output voltage and/or outputcurrent from the battery cells 212, 214, 216, and 218.

According to another embodiment, the terminals 202 and 204 may becoupled to other battery pack system modules in parallel or series (asshown below with reference to FIG. 3). According to one embodiment, thebattery cells 212, 214, 216, and 228 may be electrochemical cells suchas lithium ion (Li-ion) battery cells, nickel-metal hydroxide (NiMH)battery cells, nickel cadmium (NiCd) battery cells, lead-acid batterycells, or a combination thereof. The battery cells may also includecapacitors or super capacitors.

Balancing enable transistors 222, 224, 226, and 228 activate intra-cellbalancing for each of the battery cells 212, 214, 216, and 218,respectively. For example, when balancing enable transistor 222 isactivated the battery cell 212 may discharge through a resistor tobalance with the battery cells 214, 216, and 218. Each of the balancingenable transistor 222, 224, 226, and 228 may be controlled throughbalancing enable signals 232, 234, 236, and 238, respectively. Thebalancing enable signals 232, 234, 236, and 238 may be controlled by amicroprocessor 206. Further details of intra-module balancing within abattery pack system module is described in U.S. patent application Ser.No. 12/195,274 (published as U.S. Patent Application Publication No.2008/0309288) entitled “Method for Balancing Lithium Secondary Cells andModules” filed on Aug. 20, 2008, to Benckenstein et al., which is herebyincorporated by reference.

An analog controller 208 measures characteristics, current status, andvoltages of the battery cells 212, 214, 216, and 218 through circuits260, 262, 264, 266, and 268. According to one embodiment, the circuits260-268 are a combination of a resistor and a capacitor such as an RCcircuit. The analog controller 208 may be powered by the battery cells212, 214, 216, and 218 through a line 284 and/or through an externalcharger (not shown) through a voltage regulator 258. The microprocessor206 may enable or disable the balancing enable signals 232, 234, 236,and 238 by receiving information about the battery cells 212, 214, 216,and 218 from the analog controller 208 through a communication bus 242such as an I²C bus. The microprocessor 206 may also receive informationfrom the analog controller 208 through an analog signal 246. Accordingto one embodiment, the microprocessor 206 is powered by a voltageregulator within the analog controller 208 through a line 278. Theanalog controller 208 may also monitor for short circuits within thebattery cells 212, 214, 216, and 218.

According to one embodiment, the microprocessor 206 may issue commandsto the analog controller 208 through the bus 242 for the analogcontroller 208 to output signals on the analog line 246 proportional tothe output voltage of one of the battery cells 212, 214, 216, and 218and read battery cell voltages from the analog line 246. Ananalog/digital converter (not shown) may be coupled between themicroprocessor 206 and the analog line 246. The analog/digital convertermay have a resolution selected to match a desired sensitivity forreceiving voltages from the analog controller 208. For example, theanalog/digital converter may be an 8-bit, 12-bit, 16-bit, 20-bit, or24-bit converter. According to one embodiment, the microprocessor 206may use information measured from the analog controller 208 in a gasgauging algorithm.

A zener diode 276 and a current limiting resistor 282 may be coupledbetween the terminals 202 and 204 to allow low current inter-modulebalancing between the battery pack system module 200 and other batterypack system modules (not shown). Further details of inter-modulebalancing with the zener diode 276 and current limiting resistor 282 isdescribed in U.S. patent application Ser. No. 12/417,435 (published asU.S. Patent Application Publication No. 2009/0289599) entitled “Systemfor Balancing a Plurality of Battery Pack System Modules Connected inSeries” filed on Apr. 2, 2009, to White et al., which is herebyincorporated by reference.

A discharge switch 254 may be coupled in series with the battery cells212, 214, 216, and 218 and the terminal 202. According to oneembodiment, the discharge switch 254 is a field effect transistor (FET)having its body diode oriented to block discharge current from thebattery cells 212, 214, 216, and 218. The discharge switch may becontrolled by the analog controller 208.

A charge switch 252 may be coupled in series with the battery cells 212,214, 216, and 218 and the terminal 202. According to one embodiment, thecharge switch 252 is a FET having its body diode oriented to blockcharge current to the battery cells 212, 214, 216, and 218. The chargeswitch may be controlled by the analog controller 208. According to oneembodiment, a driver 256 is coupled between the charge switch 252 andthe analog controller 208.

A module bypass switch 240 may be coupled in parallel with the terminals202 and 204 such that when the switch 240 is activated, substantiallyall current through the battery pack system module 200 flows through theswitch 240. According to one embodiment, the switch 240 is a FETcontrolled by the analog controller 208. In another embodiment, theswitch 240 is controlled by the microprocessor 206 through the analogcontroller 208. In yet another embodiment, the switch 240 is connectedto the microprocessor 206 and receives commands directly from themicroprocessor 206. In a further embodiment, the switch 240 is connectedto the bypass detection circuit 272 and receives commands from themicroprocessor 206 through the bypass detection circuit 272. The switch240 may be activated when other battery pack system modules (not shown)in a battery pack system are unbalanced with the module 200. Forexample, when the battery pack system module 200 is charged to a higherlevel of charge than other battery pack system module coupled to themodule 200, the module bypass switch 240 may be activated to supplycharge current to other modules to bring the other modules into balancewith the module 200. The microprocessor and/or the analog controller 208may activate the switch 240 when a configurable voltage is measuredacross the terminals 202 and 204. The microprocessor 206 and/or theanalog controller 208 may make decisions for operating the switch 240with information received from a module bypass switch detection circuit272, described below. Additionally, the microprocessor 206 and/or theanalog controller 208 may forward commands to the switch 240 receivedthrough an external initializer, described below.

Inter-module balancing may be performed by de-activating the chargeswitch 252 to reduce to little or none the charging current flowingthrough the battery cells 212, 214, 216, and 218. After the chargeswitch 252 is de-activated inter-module balancing may be performedthrough the diode 276. Higher inter-module balancing currents may beobtained by activating the module bypass switch 240. Before the switch240 is activated, the discharge switch 254 may be de-activated toprevent shorting of the battery cells 212, 214, 216, and 218. Afterde-activating the discharge switch 254, the module bypass switch 240 maybe activated to allow charging current to bypass the module 200. Afterthe module 200 has reached balance with other modules in the batterypack system, the module bypass switch 240 may be de-activated followedby activation of the charge switch 252 and of the discharge switch 254.

The charge switch 252, the discharge switch 254, and the module bypassswitch 240 may be controlled through the analog controller 208 by themicroprocessor 206. For example, the microprocessor 206 may issuecommands over the bus 242 to activate or de-activate the switches 252,254, and 240. The microprocessor 206 may issue commands to maintainbalance between the battery pack system module 200 and other batterypack system modules. According to one embodiment, the microprocessor 206is configured with information about the battery cells 212, 214, 216,and 218 and/or applications for using the module 200. For example, themicroprocessor 206 may have information regarding open circuit voltagecurves for and/or physical chemistry of the battery cells 212, 214, 216,and 218. According to another embodiment, the microprocessor 206 mayhave application information such as whether the module 200 isconfigured for use in a vehicle including load information. Themicroprocessor 206 may use the battery cell information and/or loadinformation in determining operation of the switches 252, 254, and 240.

According to one embodiment, a Schottky diode 290 is coupled between theterminals 202 and 204. The Schottky diode 290 may prevent damage to thebattery pack system module 200 from low voltage transients occurring atthe terminal 202. The Schottky diode 290 may also carry bypass currentfrom the terminal 202 to the terminal 204 before the switch 240 isactivated. Further, a reverse voltage across the Schottky diode 290 maybe measured by the microprocessor 206 and/or the analog controller 208and used to decide when to activate the switch 240. According to anotherembodiment, a current-limiting transient voltage suppression (TVS) diode292 is coupled between the terminals 202 and 204. The diode 292 mayprevent damage to the battery pack system module 200 from high voltagetransients at the terminal 202. According to another embodiment, thebattery pack system module 200 may include both the Schottky diode 290and the diode 292.

According to one embodiment, a fuse 270 is coupled in series between thedischarge switch 254 and the battery cells 212, 214, 216, and 218. Thefuse 270 prevents damage to the battery cells 212, 214, 216, and 218 inthe event of a failure in the discharge switch 254.

The module bypass switch detection circuit 272 may be coupled inparallel with the module bypass switch 240. The detection circuit 272may measure the voltage across the bypass module switch 240. Accordingto one embodiment, the voltage is measured as the voltage between theterminals 202 and 204 and a battery voltage measured between theterminal 202 and the line 284. The module bypass detection circuit 272may also detect reverse voltage conditions in the battery pack systemmodule 200. When a low state of charge is reached in the battery packsystem module, the discharge switch 254 may be de-activated to preventover discharge of the battery pack system module 200. The diode 276 mayallow discharge current to continue to pass through the battery packsystem module 200 after the discharge switch 254 is de-activated. Thismay cause a reverse voltage to develop across the diode 276. The modulebypass detection circuit 272 may detect the reverse voltage conditionand activate the module bypass switch 240 to allow discharge current topass through the battery pack system module 200. According to oneembodiment, the diode 276 may be optional. In this embodiment, a reversevoltage may be measured across the Schottky diode 290 as describedabove.

The microprocessor 206 may also monitor the battery pack system module200 through a thermistor 274 and a current sensing resistor 250. Thethermistor 274 and the current sensing resistor 250 may be included in apack sensing circuit. The thermistor 274 allows the microprocessor 206to monitor the temperature of the module 200. The microprocessor 206 mayuse information about the temperature of the module 200 to activate orde-activate the module bypass switch 240, the charge switch 252, and/orthe discharge switch 254 or combinations thereof. The microprocessor 206may also use information from the current sensing resistor 250 tomonitor the charge status of the battery cells 212, 214, 216, and 218.For example, the microprocessor 206 may perform Coulomb counting withthe current sensing resistor 250. The microprocessor 206 may be coupledto the thermistor 274 and the current sensing resistor 250 through ananalog-to-digital converter (not shown) selected to match a desiredsensitivity for measurements.

The microprocessor 206 and the analog controller 208 may form acontroller assembly. The controller assembly communicates through a bus244. The bus 244 may be, for example, an RS-232 or RS-485 bus. Accordingto one embodiment, the microprocessor 206 receives a module enablesignal 248 to enable or disable the module 200. The bus 244 may be usedby the microprocessor 206 and/or the analog controller 208 to reportcurrent measured from the current measurement resistor 250, to reportover-charge or over-discharge currents, to report a temperature measuredby the thermistor 274, to report Coulombs counted for the battery cells212, 214, 216, and 218, and/or to report status of the charge switch252, the discharge switch 254, and the module bypass switch 240.

According to one embodiment, the bus 244 includes isolation circuits(not shown). The isolation circuits may optically or digitally isolate avoltage on the bus 244 from voltages within the battery pack systemmodule 200.

According to one embodiment, the microprocessor 206 may also receive areset signal (not shown). The reset signal may be a separate lineconnection such as the module enable signal 248 or the reset signal maybe received over the bus 244. The reset signal allows for restartingand/or troubleshooting the microprocessor 206. The microprocessor 206may also include other debugging functionality available through the bus244 or other line connection.

FIG. 3 is a block diagram illustrating an exemplary battery pack systemhaving series and parallel coupled battery pack system modules accordingto one embodiment. A battery pack system 300 includes first modules 320a, 320 b, . . . , 320 h coupled in series with each other. The system300 also includes second modules 322 a, 322 b, . . . , 322 h, thirdmodules 324 a, 324 b, . . . , 324 h, fourth modules 326 a, 326 b, . . ., 326 h, and fifth modules 328 a, 328 b, . . . , 328 h. Each of themodules of the second modules 322 are coupled in series with each otherand the third modules 324, fourth modules 326, and fifth modules 328 aresimilarly coupled in series. The first modules 320, second modules 322,third modules 324, fourth modules 326, and fifth modules 328 are coupledin parallel between a negative terminal 302 and a positive chargeterminal 304 and a positive discharge terminal 306. Diodes 308 a, 308 b,. . . , 308 e are coupled between the positive charge terminal 304 andthe modules 320, 322, 324, 326, and 328. Diodes 310 a, 310 b, . . . ,310 e are coupled between the positive discharge terminal 306 and themodules 320, 322, 324, 326, and 328. The diodes 308 and 310 may beisolation diodes to prevent any of the first modules 320, second modules322, third modules 324, fourth modules 326, and fifth modules 328 fromdischarging any other of the modules 320, 322, 324, 326, and 328.

Each of the modules of the first modules 320, second modules 322, thirdmodules 324, fourth modules 326, and fifth modules 328 may include amodule bypass switch as described above with reference to FIG. 2 andother balancing circuits as described in U.S. patent application Ser.No. 12/417,435. Inter-module balancing may be effected through the useof the module bypass switch in the modules 320, 322, 324, 326, and 328.For example, if the module 320 e is at a higher charge than the module320 d, the module 320 e may de-activate a charge switch, de-activate adischarge switch, and activate a module bypass switch in the module 320e to allow charge current to flow to the module 320 d. The current mayalso flow to the modules 320 a-c and 320 f-h that have not activatedtheir module bypass switches through the series connection of modules320. Control of inter-module balancing may be performed within each ofthe modules 320, 322, 324, 326, and 328 as described below withreference to FIG. 4 or by an initializer (not shown), by a client device(not shown), or by a master battery system pack module described belowwith reference to FIGS. 5 and 6.

The battery pack system 300 may be charged through a power supply (notshown) coupled to the positive charge terminal 304 and the negativeterminal 302. According to one embodiment, the power supply may be aconstant-current constant-voltage power supply. According to otherembodiments, the power supply 332 may be a fuel cell, a solar cell, orcombinations thereof.

Although FIG. 3 illustrates five parallel coupled groups of eight seriesconnected battery pack system modules, a battery pack system mayincorporate any number of battery pack system modules in series orparallel. The battery pack system modules in a battery pack system maybe of similar capacity, similar output voltage, and/or similar outputcurrent, or have different capacities, different output voltages, and/ordifferent output currents. Additionally, the diodes 308 and 310 of FIG.3 may be coupled on a high potential or low potential end of the modules320, 322, 324, 326, and 328.

According to one embodiment, the isolation diodes 308 and 310 may beremoved and the modules 320, 322, 324, 326, and 328 are charged anddischarged from a single port rather than the ports 304 and 306. Inanother embodiment, the modules 300, 322, 324, 326, and 328 may beconnected in parallel through connections in between the port 302 andthe ports 304 and 306. For example, the modules 320 g, 322 g, 324 g, 326g, and 328 g may be coupled in parallel with each other. Likewise, oneor more other sets of modules 320-328 a, 320-328 b, etc. may be coupledin parallel.

FIG. 4 is a flow chart illustrating an exemplary method of charging abattery pack system module according to one embodiment. A flow chart 400begins at block 402 by determining if the battery pack system module hasreached a first criteria. According to one embodiment, the firstcriteria is a level of charge. According to other embodiments, the firstcriteria may be a battery cell temperature, a battery cell voltage, orother measurable characteristics of the battery cell. If the firstcriteria is not reached, the flow chart returns to block 402 until thefirst criteria is met.

When the first criteria is reached, the charge switch is de-activated atblock 404. At block 406, the voltage across the battery pack systemmodule's terminals are determined to exceed a first voltage value. Ifthe voltage across the battery pack system module's terminals has notexceeded a certain first voltage value, the flow chart returns to block406. According to one embodiment, the first voltage value of block 406may be determined from the voltage of the power supply, the voltage ofthe battery pack system modules in the battery pack system, and/or thenumber of battery pack system modules or a combination of these. Thefirst voltage value may be configured as a value specific to aparticular battery pack system configuration. After the charge switchvoltage exceeds a certain voltage value, the discharge switch isde-activated at block 408 and a module bypass switch is activated at410. Thus, charge current is allowed to pass through the battery packsystem module through a low resistance path without discharging thebattery cells of the module.

A timer may be started after activating the module bypass switch, and,when a certain time period has passed at block 412, the module bypassswitch is de-activated at block 414. The charge switch and dischargeswitch may be re-activated at block 416.

According to one embodiment, the method 400 may be executing within amicroprocessor or controller assembly in parallel with other processes.For example, other processes may monitor parameters such as temperature,state of charge, and charge or discharge current. The other processesmay also issue commands to the charge switch, discharge switch, and/ormodule bypass switch. For example, one of the other processes mayactivate the charge switch while the method 400 is looping at block 406.In this example, the charge switch may be again de-activated at block408.

The method of FIG. 4 provides for inter-module balancing of a batterysystem by allowing a battery pack system module to have autonomouscontrol over charging of battery cells within each respective batterypack system module without communication to a central computer.According to another embodiment, the battery pack system module may bein communication with an initializer, such as a microcontroller, forcontrolling the balancing of battery pack system modules within abattery pack system. The method of FIG. 4 may be used in combinationwith a separate method for activating a module bypass switch executed bya bypass detection circuit, such as the bypass detection circuit 272described above. When used in combination with a bypass detectioncircuit, a microprocessor programmed to perform the steps of FIG. 4 mayallow a configurable voltage for activating a module bypass switch inaddition to the voltage that activates the bypass detection circuit.

FIG. 5 is a block diagram illustrating an exemplary battery pack systemhaving a plurality of battery pack system modules according to oneembodiment. A system 500 includes a battery pack system 502 havingbattery pack system modules 504 a, 504 b, 504 c. The battery pack systemmodule 504 a includes a controller assembly 510 for interfacing with abus 540 and components within the battery pack system module 504 a. Thecontroller assembly 510 may include analog controllers, digitalcontrollers, and/or microprocessors. According to one embodiment, thebattery pack system module 504 a includes an isolated bus interface 524for isolating the battery pack system module 504 a from the bus 540,which may be operating at a different potential.

The controller assembly 510 may interface with a module bypass detectorcircuit 512 and module bypass switch 514. By sensing an output from themodule bypass detector circuit 512, the controller assembly maydetermine when to activate and de-activate the module bypass switch 514and a disconnect circuit 516. The disconnect circuit 516 may include acharge switch and a discharge switch. The controller assembly 510 mayalso interface with a pack sensing circuit 518 and the disconnectcircuit 516. The pack sensing circuit 518 may report to the controllerassembly 510 characteristics of battery cells (not illustrated) locatedwithin the battery pack system module 504 a. For example, the packsensing circuit 518 may monitor charge levels of the battery cells withCoulomb counters or battery cell temperatures with thermistors. Thecoulomb counters and/or thermistors may interface with the controllerassembly 510 through an analog/digital converter (ADC). The controllerassembly 510 may use information obtained from the pack sensing circuit518 to determine activation and de-activation of a charge switch and adischarge switch within the disconnect circuit 516.

Additionally, the battery pack system module 504 a may include aninternal display 522 to communicate with an operator of the battery packsystem 502 a status of the battery pack system module 504 a. Forexample, the battery pack system module 504 a may include a lightemitting diode (LED) indicating the status of the module bypass switch514. In another example, the internal display 522 may be a liquidcrystal display (LCD) indicating the charge level of battery cellswithin the battery pack system module 504 a.

An initializer 542 coupled to the bus 540 may communicate with each ofthe battery pack system modules 504 a, 504 b, 504 c. The initializer 542may accumulate information from each of the battery pack system modules504 a, 504 b, 504 c to make decisions regarding the charging operationof the battery pack system modules 504 a, 504 b, 504 c. For example, bymonitoring the charge levels of the different battery pack systemmodules 504 a, 504 b, 504 c, the initializer 542 may instruct anunbalanced battery pack system module to activate the module bypassswitch. According to one embodiment, the initializer 542 may be coupledto an external display device (not shown) for displaying the status ofthe battery pack system 502 and/or receiving operator commands for thebattery pack system 502. The initializer 542 may monitor the batterypack system 502 for one or more events such as, for example, health ofthe battery cells, capacity of the battery cells, overcharge, overdischarge, over current, short circuit current, over temperature, undertemperature, state of charge of the battery cells, and/or balance of thebattery cells. According to one embodiment, the initializer 542 may beprogrammed with new computer instructions or configuration settingsthrough, for example, a flash update to an EEPROM chip storing computerinstructions in the initializer 542. In another embodiment, theinitializer 542 may download new computer instructions and/orconfiguration data into the controller assembly 510.

According to one embodiment, the initializer 542 may have control of allinternal cell balancing circuits within a module for intra-modulebalancing and low current precision inter-module balancing, as well ascontrol over the module bypass switch for each of the modules foraccurate high current inter-module balancing. Thus, the initializer mayperform inter-module balancing and intra-module balancing. Thecombination of inter-module balancing and intra-module balancing allowscontinuous balancing in any battery mode including charge mode,discharge mode, quiescent mode, and storage mode. For example, theinitializer 542 may activate all intra-module discharge balancingcircuits in a module in order to balance the module with other modules.

The initializer 542 may be coupled to a network 544 for communicatingwith a client device 546. The initializer 542 may allow the clientdevice 546 to monitor conditions within each of the battery pack systemmodules 504 a, 504 b, 504 c and/or control components within the batterypack system modules 504 a, 504 b, 504 c. For example, an operator at theclient device 546 may instruct the initializer 542 to activate themodule bypass switch 514 of the battery pack system module 504 a. Inanother example, an operator at the client device 546 may adjustsettings within the initializer 542 such as current limits, voltagelimits, temperature limits, charge levels, and/or balancing settings. Inyet another example, an operator at the client device 546 may collectstatus and data from all of the battery pack system modules on the bus540 for real-time continuous display of the complete battery system andfor setting and resetting battery system audio and visual alarms.

According to one embodiment, the initializer 542 may be removed from thesystem 500 by designating the controller assembly 510 of the batterypack system module 504 a, or another one of the battery pack systemmodules 504 a, 504 b, 504 c, to function as a master controller. Themaster controller communicates with other battery pack system modulecontroller assemblies and may provide access for an operator on a clientdevice, an internal display, and/or an external display.

FIG. 6 is a block diagram illustrating a client device for an exemplarybattery pack system according to one embodiment. A computer system 600includes a central processing unit (CPU) 602 coupled to a system bus604. The CPU 602 may be a general purpose CPU or microprocessor,graphics processing unit (GPU), microcontroller, or the like. Thepresent embodiments are not restricted by the architecture of the CPU602 so long as the CPU 602, whether directly or indirectly, supports themodules and operations as described herein. The CPU 602 may execute thevarious logical instructions according to the present embodiments.Logical instructions may be stored in the CPU 602, in a battery packsystem module (not shown), or in an initializer (not shown).

The computer system 600 may also include random access memory (RAM) 608,which may be, for example, SRAM, DRAM, SDRAM, or the like. The computersystem 600 may use RAM 608 to store the various data structures used bya software application having code to electronically monitor and controlbattery pack system modules. The computer system 600 may also includeread only memory (ROM) 606 which may be PROM, EPROM, EEPROM, opticalstorage, or the like. The ROM may store configuration information forbooting the computer system 600. The RAM 608 and the ROM 666 hold userand system data.

The computer system 600 may also include an input/output (I/O) adapter610, a communications adapter 614, a user interface adapter 616, and adisplay adapter 622. The I/O adapter 610 and/or the user interfaceadapter 616 may, in certain embodiments, enable a user to interact withthe computer system 600 in order to input operating parameters for abattery pack system module. In a further embodiment, the display adapter622 may display a graphical user interface for monitoring and/orcontrolling battery pack system modules. The display adapter 622 orother user interface device on the bus 604 may include audio outputs andhigh visibility visual displays for audibly and/or visually alerting auser to battery system status; especially status that requires priorityresponse from a user.

The I/O adapter 610 may connect one or more storage devices 612, such asone or more of a hard drive, a compact disk (CD) drive, a floppy diskdrive, and a tape drive, to the computer system 600. The communicationsadapter 614 may be adapted to couple the computer system 600 to anetwork, which may be one or more of a LAN, WAN, and/or the Internet.The user interface adapter 616 couples user input devices, such as akeyboard 620 and a pointing device 618, to the computer system 600. Thedisplay adapter 622 may be driven by the CPU 602 to control the displayon the display device 624.

The applications of the present disclosure are not limited to thearchitecture of computer system 600. Rather the computer system 600 isprovided as an example of one type of computing device that may beadapted to perform the functions of a client device 546. For example,any suitable processor-based device may be utilized including withoutlimitation, personal data assistants (PDAs), tablet computers,smartphones, computer game consoles, or multi-processor servers.Moreover, the systems and methods of the present disclosure may beimplemented on application specific integrated circuits (ASIC), verylarge scale integrated (VLSI) circuits, or other circuitry. In fact,persons of ordinary skill in the art may utilize any number of suitablestructures capable of executing logical operations according to thedescribed embodiments.

External control of a battery pack system with an initializer may beperformed when the initializer communicates with controller assemblieswithin the battery pack system modules. FIG. 7 is a flow chartillustrating an exemplary method of charging a battery pack systemaccording to one embodiment. A flow chart 700 begins at block 702 wherean initializer decides if a battery pack system module has becomeunbalanced with other battery pack system modules within a battery packsystem. In one example, the battery pack system module may be determinedto be charged to a higher level than other battery pack system modulesin the battery pack system. If a battery pack system is unbalanced theflow chart continues to block 704. At block 704 the charge switch in theunbalanced battery pack system module may be de-activated to preventfurther charging of battery cells within the unbalanced battery packsystem module. Additionally, at block 704 the discharge switch isde-activated to prevent shorting of the battery cells when the modulebypass switch is activated. At block 706 the module bypass switch forthe unbalanced battery pack system module is activated.

At block 708 it is determined if the battery pack system modules havereached a balanced state with the unbalanced battery pack module. Whenbalance is reached, the flow chart continues to block 710. At block 710the module bypass switch for the previously unbalanced battery packsystem module is de-activated. At block 712 the charge switch and thedischarge switch for the previously unbalanced battery pack systemmodule are activated. The method illustrated in FIG. 7 may be performedby an initializer, a client device, or a battery pack system moduleconfigured as a master module to control other modules. When theinitializer, client device, or master module is coupled to a display ora client device, software may be executed to display a user interfacefor monitoring and/or controlling the battery pack system.

FIG. 8 is a block diagram illustrating a software application formonitoring a battery pack system according to one embodiment. A softwareapplication 800 may include displays 810, 820 for monitoring batterypack system modules inside of a battery pack system. The displays 810,820 may include information such as, for example, temperature, chargelevel, voltage, status of the module bypass switch, and/or alerts (notshown) for each battery pack system module in the battery pack system.Additionally, the software application 800 may include buttons 812, 822for activating module bypass switches within the battery pack systemmodules monitored in displays 810, 820, respectively. Charge switchesand/or discharge switches may be activated and de-activatedautomatically by the software when the buttons 812 and 822 are actuated.According to one embodiment, the display also includes separate buttons814 and 824 for activating and de-activating a charge switch of eachmodule and buttons 816 and 826 for activating and de-activating adischarge switch of each module. The software application 800 may bestored on a computer readable medium such as, for example, a compactdisc (CD), a hard disk drive (HDD), a digital versatile disc (DVD),flash memory, or the like.

The battery pack system of the present disclosure allows balancing ofbattery pack system modules within the battery pack system with a modulebypass switch, charge switch, and discharge switch. The module bypassbalancing process may be performed continuously during charging ordischarging of the battery pack system modules resulting in increasedlife from the battery pack system modules and reduced safety hazardsfrom unbalanced battery pack system modules. Balancing times may bereduced with the module bypass switch, charge switch, and dischargeswitch because of higher charging or discharging balancing currentpassing through the modules. The faster balancing times may be achievedwith little or no additional heat dissipation in the battery pack systemmodule. Reducing the heat dissipation prevents dangerous conditions fromdeveloping in the battery pack system module.

Faster balancing may be particularly advantageous when replacing batterypack system modules. For example, if one of the battery pack systemmodules is replaced, the replacement battery pack system module may berapidly brought into balance with other battery pack system modules byactivating module bypass switches, charge switches, and dischargeswitches to direct charge current to the unbalanced battery pack systemmodules.

According to another embodiment, the bypass current through the modulebypass switch may be monitored and used to determine when to activateand/or deactivate the module bypass switch. FIG. 9 is a circuitschematic illustrating an exemplary battery pack system module havingcharge, discharge, and module bypass switches and bypass switch currentmonitoring according to one embodiment. A battery pack system module 900is similar to the battery pack system module 200 of FIG. 2. However, themodule bypass switch 240 is coupled to the current sensing resistor 250.When the module bypass switch 240 is activated current bypasses thebattery cells 212, 214, 216, and 218. Instead, current flowssubstantially through the module bypass switch 240 and the currentsensing resistor 250 from the terminal 202 to the terminal 204.

When bypass current flows through the current sensing resistor 250, themicroprocessor 206 may measure a voltage across the current sensingresistor 250 and calculate a value for the magnitude of the bypasscurrent. For example, the microprocessor 206 may receive a value from ananalog to digital converter (not shown) coupled between the currentsensing resistor 250 and the microprocessor 206. The microprocessor 206may use information about the value of the bypass current flowingthrough the module bypass switch 240 to instruct the analog controller208 to activate and/or de-activate the module bypass switch 240.Although the current sensing resistor 250 is illustrated in FIG. 9 formeasuring bypass current through the module bypass switch 240, othercurrent measurement devices may be used instead.

One method for programming the microprocessor 206 for monitoring thebypass current through a current measurement device is described withreference to FIGS. 10A-B. FIGS. 10A-B are a flow chart illustrating anexemplary method of charging a battery pack system module with bypassswitch current monitoring according to one embodiment. A method 1000begins at block 402 with determining if a battery pack system module hasreached a first criteria. When the battery pack system module hasreached a first criteria the method 1000 continues to block 404 withde-activating a charge switch.

The method 1000 continues to block 1006 with determining whether thevoltage across the module bypass switch exceeds a first voltage value.If the module bypass switch has not exceeded the first voltage value,the flow chart returns to block 1006. After the module bypass switchvoltage exceeds the first voltage value, the discharge switch isde-activated and the charge switch is de-activated at block 1008 and amodule bypass switch is activated at block 1010. As described above, thecharge switch may be de-activated at block 1008 after block 1004 becausea separate process may have activated the charge switch. Thus, chargecurrent is allowed to pass through the battery pack system modulethrough a low resistance path without discharging the battery cells ofthe module.

At block 1020 the bypass current passing through the module bypassswitch is measured. As long as the bypass current exceeds a thresholdvalue the method 1000 remains at block 1020. When the bypass currentfalls below the threshold value another battery pack module in theseries of battery pack modules may have opened its module bypass switch.By monitoring for this decrease in bypass current the battery packsystem module may determine when it has reached a similar state ofcharge as other battery pack system modules it is in series with. Forexample, if any other battery pack system modules in series with thebypassed battery pack system module opens its charge switch this willresult in stopping all charge current to all of the series connectedmodules with the exception of a moderate amount of 2 mA current to powerthe battery pack system modules' control circuits, in addition to apossible 150 mA current through the modules' zener diode bypass circuits(e.g., diode 276 and diode 282 of FIG. 2) and a possible 50 mA ofcurrent measurement error. In this example, an appropriate thresholdvalue may be 202 mA (e.g., 2 mA+150 mA+50 mA). After the bypass currentfalls below the threshold value the method 1000 proceeds to block 1014with de-activating the module bypass switch and to block 1016 withactivating the charge switch and activating the discharge switch.Although not shown, a method of operating a microprocessor formonitoring bypass current may include additional steps as describedabove including, for example, remote monitoring of the bypass current.

According to one embodiment a microprocessor programmed according to themethod 1000 may utilize additional information for making decisionsregarding activating and/or de-activating the bypass current switch, thecharge switch, and the discharge switch. For example, the microprocessormay utilize information such as an amount of time the module bypassswitch has been activated in deciding when to activate or de-activatethe module bypass switch.

Monitoring bypass current for controlling module bypass switch operationas described in FIGS. 9 and 10A-B may provide additional advantages overa timer based method as described in FIGS. 2 and 4. By monitoring thebypass current a battery pack system module may acquire informationregarding other battery pack system modules coupled to it. Theinformation inferred about other battery pack system modules through thebypass current monitoring does not require communications between thebattery pack system modules, which may increase the cost and complexityof the battery pack system modules. When the battery pack system modulehas information about the state of charge of other battery pack systemmodules, the battery pack system module may make more informeddecisions. In fact, the battery pack system modules may performautonomous inter-module balancing by monitoring the bypass currentthrough the module bypass switch.

The additional information and autonomous behavior may increase thespeed and/or accuracy with which the battery pack system modules becomebalanced. For example, accuracy of inter-module balancing may improvefrom 10-15% error without bypass current monitoring to 2-3% with bypasscurrent monitoring. Accuracy of the inter-module balancing refers to thedifference in state of charge between battery pack system modules whenthe balancing process has completed. That is, without bypass currentmonitoring the inter-module balancing may only achieve a charge statefor the battery pack system modules within 10% of each other. Withbypass current monitoring, inter-module balancing may achieve a chargestate for the battery pack system modules with 2% of each other.

By achieving a more accurate coarse balancing of the battery pack systemmodules a quicker balancing of the battery pack system modules may beobtained. After coarse balancing of the battery pack system modulesthrough inter-module balancing with the module bypass switches of thebattery pack system modules, fine balancing of the battery pack systemmodules follows to bring the battery pack system modules closer to abalanced state. Fine balancing is a slower process than coarse balancingand, thus, the more accurate balance obtained with coarse balancing theless time consumed for fine balancing mode. For example, consideringbattery pack system modules with a total capacity of 100 Amp-hours and afine balancing rate of 100 milliAmps/hour, balancing battery pack systemmodules with fine balancing after coarse balancing achieves 10% accuracymay take one or more days. Balancing the same battery pack systemmodules with fine balancing after achieving 2% accuracy withinter-module balancing with current bypass monitoring may consume only afew hours. Thus, inter-module balancing with current bypass monitoringimproves availability of battery pack system modules by decreasing thetime consumed balancing the battery pack system modules.

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutions,and alterations can be made herein without departing from the spirit andscope of the disclosure as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods, and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thepresent disclosure, processes, machines, manufacture, compositions ofmatter, means, methods, or steps, presently existing or later to bedeveloped that perform substantially the same function or achievesubstantially the same result as the corresponding embodiments describedherein may be utilized according to the present disclosure. Accordingly,the appended claims are intended to include within their scope suchprocesses, machines, manufacture, compositions of matter, means,methods, or steps.

What is claimed is:
 1. An apparatus, comprising: a first battery packsystem module, comprising: a battery cell coupled between a firstterminal and a second terminal; a charge switch coupled in series withthe battery cell and the first terminal for interrupting charging of thebattery cell; a discharge switch coupled in series with the chargeswitch and the first terminal for interrupting discharging of thebattery cell; a module bypass switch for shorting the first terminal andthe second terminal; and a current measurement device coupled betweenthe module bypass switch and at least one of the first terminal and thesecond terminal.
 2. The apparatus of claim 1, further comprising a zenerdiode in series with a resistor, the zener diode and the resistor inparallel with the module bypass switch.
 3. The apparatus of claim 1, inwhich the module bypass switch is a field effect transistor (FET). 4.The apparatus of claim 1, further comprising a second battery packsystem module coupled in series with the first battery pack systemmodule.
 5. The apparatus of claim 1, further comprising: a controllerassembly coupled to the charge switch, the discharge switch, the modulebypass switch, and the current measurement device; a bus coupled to thecontroller assembly; and an initializer coupled to the bus.
 6. Theapparatus of claim 5, further comprising a pack sensing circuit coupledto the controller assembly.
 7. The apparatus of claim 5, furthercomprising a fuse coupled between the discharge switch and the batterycell.
 8. The apparatus of claim 5, further comprising an isolated businterface coupled between the bus and the controller assembly.
 9. Theapparatus of claim 5, in which the controller assembly is configured tomonitor a bypass current through the module bypass switch by measuringthe bypass current from the current measuring device.